Manually Inputting Mail Merge Links

Hi everyone!
I have lots of similar excel documents and happily mail merge to Word using the mail merge wizard successfully.

My problem is I want to create one Word document (like a template) that can be used with all the Excel documents, this would work for the generic columns/fields. BUT... there are a quite few columns (fields) that differ on each document and it's a pain to keep inserting them on to every document.

Is there a way of manually typing in the mail merge link?

I have tried using formulas in Excel to replicate the mail merge links using the columns headers and adding in the mergefield so they are in the format of what the mail merge wizard automatically inserts. The problem is none of the links are 'active' and when the merge starts they remain as text in the Word document.

Hope this isn't to confusing